In general, known methods are referred to as MAC (Message Authentication Code) methods. In cryptography, the MAC method is used for the authentication of a transmitted message, and thus to protect against undetected manipulation of the transmitted message. For example, such methods are used in the Internet (e-mail, online banking), or also in chip cards, where signatures are used to secure the integrity of the data. In the known MAC methods, the data that are to be transmitted are successively encrypted block by block; in particular in CBC-MAC methods, the encrypted data of a block are each antivalently linked to the next data block and the data thus obtained are then re-encrypted. The so-called MAC is transmitted/communicated to the receiver in addition to the data, as a test part. The generation of the test part takes place using a secret key that is also available in the receiver. In this way, in the receiver the data can be subjected to the same procedure as in the transmitter, the same secret key being used to generate a test part for verification, i.e. a verification test part. If comparison of the verification test part with the test part results in agreement, it can be concluded that the transmitted data are intact.